Some houses have a little rectangular area just inside the front door. You then walk through that little area to get into the main areas of the house. This little area is well defined with a wall on either side, with the front door behind you.

If it has a wall and another door, then it's a room (a mud room). Otherwise you can call it the entry or if you want fancy, foyer (which has two possible pronunciations). (US English)
– aparente001Jun 14 at 2:55

In the UK this would most commonly be called a hall assuming it has doors, arches or similar leading into other rooms. A hall is normally a long, often narrow, room with several rooms opening off it (corridor is rarely used inside the home) but the minimal hall is probably the one I had in my old house: about 1 metre square, with the front door living room door and stairs leading from it.

As to whether it's considered a room, that's variable. When thinking about decorating, for example, yes - "which room are you going to decorate next?", "The hall". But in terms of counting rooms to describe the size of the house, generally a hall isn't a room. Wider examples may be an exception to this - some are big enough to use a corner as an office or seating area.